Adulteration of beetroot red and paprika extract based food colorant with Monascus red pigments and their detection by HPLC-QTof MS analyses

Abstract

An intense red food colorant found as a wholesale good for the European market and claimed as a mixture of beetroot red and paprika extract was investigated. The vibrant color intensity could not be readily explained because the measured amounts of dyes typical for beetroot red and paprika extract were too low. These facts led to the question of the source of the intense color, which is the focus of the present work. Efforts were made in the development of high performance liquid chromatography (HPLC) hyphenated with high resolution quadrupole/time-of-flight tandem mass spectrometry (QTof MS). Additional red color compounds could be detected and were identified as Monascus red pigments. N-leucyl-rubropunctamine and its isomer N-isoleucyl-rubropunctamine were found as the main compounds of Monascus red pigments in the food colorant. Starting from rubropunctatin, these compounds were synthesized in the lab. Chromatography and mass spectrometry confirmed unambiguously their presence in the colorant. Furthermore, an authentic sample of Monascus red pigments utilized as colorant in South East Asian countries showed excellent chromatographic and mass spectrometric agreement and confirmed the adulteration of the beetroot red and paprika extract based food colorant.